1. Field of the Invention
The present invention relates to a power circuit breaker to cut off instantaneously a power circuit with a gas pressure generated by an igniter unit to release a fuse element from a pair of interconnection terminals.
2. Related Art
FIG. 3 shows a conventional fuse 61 for cutting off a large power circuit. The fuse 61 has a synthetic resin main housing 62, a conductive metal fuse element 63 received in the main housing, and a synthetic resin cover 64 for covering an upper opening of the main housing 62.
The fuse element 63 has a generally U-shaped base plate 65, two terminals 66 each unitarily formed with the base plate 65 at one end thereof, a tin piece 67 disposed on the base plate 65 for thermal accumulation. Each terminal 66 is opposed to a resilient contact strip 68 formed separately from the fuse element 63. The terminal 66 and resilient contact strip 68 can contact a pin terminal of a fuse box (not shown) or the like. The pin terminal is inserted from a lower opening 69 of the main housing 62.
The base plate 65 is formed with a locking piece 70 extending diagonally outward. The locking piece 70 abuts against an inner shoulder of the main housing 62 to prevent the fuse element 63 from being released from the main housing 62. The base plate 65 is fused by an overcurrent to cut off an associated power circuit.
FIG. 4 is a graph showing a time required for fusing of the fuse 61. The time is a function of applied current. This fuse characteristic is obtained by a measurement devise shown in FIG. 5.
In FIG. 5, denoted 61 is a fuse, 71 a busbar connected to the fuse 61, and 72 an electrical wire connected to the busbar 71 for power supply. Two busbars 71 are fixed on a base 73 made of an insulation material. Each busbar 71 has an upward extending male terminal 74 which can be connected to the terminal 66 (FIG. 3) of the fuse 61.
As illustrated in FIG. 4, the fusing time T of the fuse 61 (FIG. 5) decreases like a quadratic curve as current I increases. Particularly, where the applied current I is comparatively small, the fusing time T increases significantly, which is shown in a zone surrounded by a phantom line A. The vertical scale for the fusing time T is logarithmic.
The conventional fuse 61, as shown in FIG. 4, requires a significantly long fusing time when the overcurrent is within a smaller range. Thus, it is difficult to cut off instantaneously an associated circuit against a smaller overcurrent. This happens also in case of an intermittent short circuit or a rare short circuit current. In addition, even in an abnormal vehicle state like a collision accident, a power circuit is not cut off when no sufficient excessive current is supplied. The conventional fuse has the disadvantages.
To solve these problems, there is proposed a power circuit breaker 76 shown in FIGS. 6 and 7.
Referring to FIG. 6, the power circuit breaker 76 has a pair of terminals 77, 78, two multi-contact-point elastic plates 80 (FIG. 7) each connected to one of the terminals 77, 78, an electrically conductive shaft 79 slidably contacting with the plates 80, and an igniter unit 81 disposed in one side of the shaft 79.
The shaft 79 is joined to a drive shaft 82 at the other end thereof. The drive shaft 82 is mounted with a torsion spring 83. The igniter unit 81 has a gas-blasting agent and a heater therein. The heater is connected to a pair of lead wires 84. The shaft 79 and the drive shaft 82 are slidably received in a housing 85 of the power circuit breaker 76.
In FIG. 6, the terminals 77, 78 each are connected to the shaft 79 by way of one of the plates 80. An overcurrent flown between the terminals 77, 78 is detected by a sensor. Successively, a current is applied to the lead wires 84, so that the heater heats up the gas blasting agent. The blasting gas pressure moves the shaft 79 in its disconnecting direction, This cuts off electrical connection between the terminals 77, 78. The torsion spring 83 urges the stopper 86 outward so that the stopper 86 abuts against the housing 85, preventing a return movement of the shaft 79.
However, the power circuit breaker 76 has disadvantages described in the following. That is, the power circuit breaker 76 has the expensive multi-contact-point elastic plates 80 connected to the terminals 77, 78 for allowing a decreased friction force. Furthermore, the power circuit breaker 76 requires parts increased in number and in cost and is complicated in configuration, because the torsion spring 83 and the stopper 86 are applied for stopping the shaft 79. In addition, the multi-contact-point elastic plates 80 make the terminals 77, 78 and the shaft 79 larger for reducing an electrical resistance between the plates 80 and the shaft 79, which tends to enlarge related parts of the power circuit breaker 76, resulted in an enlarged breaker in overall size.
Japanese Patent Application H. 10-241524 discloses a power circuit breaker (not shown) in which a gas bursting force breaks a connection substrate to cut off a power circuit. Because of this configuration, the power circuit breaker is not reusable and is not commonly applied to various uses. Moreover, the power circuit breaker has another disadvantage that its main housing including an igniter unit requires an additional fitting work to secure it by bolting.
In view of the disadvantages of the aforementioned fuse and breakers, an object of the invention is to provide a power circuit breaker which can positively cut off a power circuit even at a smaller overcurrent. The breaker also allows a reliable cut-off of the power circuit when a sensor detects an abnormal state like an unintentional heat generation state or on a vehicle collision accident. In addition, the breaker has a simplified configuration consisting of parts reduced in number. The breaker is not expensive in cost, compact, easy in assembling, reusable, and suitable for a general-purpose.
For achieving the object, a power circuit breaker according to a first aspect of the present invention includes a main housing, an igniter unit disposed in a cylindrical wall formed in the main housing, a holder disposed in the cylindrical wall so as to oppose to the igniter unit, a boss of the holder engaging with the cylindrical wall, a fuse element held by the holder, and a pair of interconnection terminals disposed in the main housing. Each end of the fuse element is electrically connected to one of the interconnection terminals.
In a second additional aspect of the present invention, the holder is locked by a locking lance formed in the main housing when each end of the fuse element has engaged with one of the interconnection terminals.
In a third additional aspect of the present invention, an activating pressure force generated by the igniter unit is larger than the sum of the stopping force of the locking lance and the friction force of the interconnection terminals to the fuse element.
In a fourth additional aspect of the present invention, the holder rests on the locking lance when the fuse element has been released from the interconnection terminals after activation of the igniter unit.
In a fifth additional aspect of the present invention, the fuse element is engaged with and stopped by an insertion hole of the holder.
In a sixth additional aspect of the present invention, the igniter unit is pressed into to be mounted in the cylindrical wall.
In a seventh additional aspect of the present invention, the interconnection terminals each are locked in the main housing with a locking piece.
In an eighth additional aspect of the present invention, the interconnection terminals each are a receptacle type terminal having two resilient contact strip portions one of which is connected to one end of the fuse element and the other of which is connected to an opposing terminal of a power circuit.
In the first aspect of the invention, the cylindrical wall can guide the boss of the holder like a cylinder-piston movement, so that the gas blasting pressure reliably forces out the holder. Thus, the breaker can rapidly cut off the power circuit even on a smaller overcurrent or on an abnormal state of the vehicle where there is no overcurrent such as collision or an unintentional heat generation in the vehicle. The igniter unit is reduced in size because of the above-mentioned construction of the holder and cylindrical wall, which makes the power circuit breaker compact. The fuse element and interconnection terminals, which are simple and not expensive, can disengage from each other to reliably cut off the power circuit because the holder retaining the fuse element is moved by the blasting pressure of the igniter unit. The power circuit breaker has more functions than the conventional large current fuse but causes no significant size increase as compared with the conventional fuse. In addition, the fuse element which is fused by a current larger than a predetermined value can cut off the power circuit on an overcurrent without ignition of the igniter unit, allowing a selective use thereof including reuse according to an application of the breaker.
In the second additional aspect of the invention, the holder is reliably retained on the housing by the locking lance while the interconnection terminals engage with the fuse element. In addition, the holder can be easily mounted on and removed from the housing.
In the third additional aspect of the invention, on ignition of the igniter unit, the locking lance positively releases the holder so that the fuse element disengages from the interconnection terminals to cut off the associated power circuit.
In the fourth additional aspect of the invention, the holder is resting on the lance when the lance has been released the holder, preventing the fuse element from unintentionally contacting the interconnection terminals to keep a cut-off state of the power circuit. The lance used for the locking and retaining of the holder is advantageous for reduction in part number and in manufacturing cost.
In the fifth additional aspect of the invention, the fuse element is S inserted into the through holes of the holder to be locked therein, allowing an easy engagement with the holder. The fuse element can be readily disengaged from the holder. The holder can be commonly used for various applications with changing the fuse element according to the associated circuit. That is, the power circuit breaker is suitable for general purpose applications, which enables standardized and reusable parts, resulted in reduction in cost of the breaker.
In the sixth additional aspect of the invention, the igniter unit is easily pushed in the cylindrical wall to be set therein. The igniter unit can be dismounted from the cylindrical wall for replacement with ease.
In the seventh additional aspect of the invention, the locking piece can readily lock the interconnection terminal in the housing. Moreover, the interconnection terminal can be removed from the housing for maintenance by releasing engagement with the locking piece.
In the eighth additional aspect of the invention, the interconnection terminals, which can electrically connect the fuse element to the lead terminals, each have the two resilient contact strip portions. The construction of the interconnection terminals is useful for reduction in part number and in manufacturing cost.